It has been required for combustors used for, e.g., gas turbines to reduce the generation of NOx (nitrogen oxide).
As described in PTL 1, premixed gas generated at a pre-mixing main nozzle is supplied to a combustor.
FIG. 10 is an example of a configuration diagram of a conventional combustor 100. The combustor 100 is configured such that a ring (hereinafter referred to as an “outlet outer ring”) 102 in an outward conical shape (also referred to as a “tapered shape” or an “enlarged conical shape”) is provided at a tip end of a combustor basket 103 in order to prevent oscillatory combustion. Moreover, in the combustor 100, premixed gas blown from a pilot burner 104 and a main burner 106 is guided along an inner wall surface 110 of a combustion liner 108 by the outlet outer ring 102.
Further, in the conventional combustor 100, part of compressed air is, as film air, supplied through the outer periphery of the outlet outer ring 102 and film air discharge holes 112 formed at the inner wall surface 110 of the combustion liner 108. In the combustor 100, a premixed gas concentration in the vicinity of the inner wall surface 110 is diluted with film air. Thus, premixed gas having reached the inner wall surface 110 of the combustion liner 108 is suppressed from combusting in the vicinity of the inner wall surface 110 of the combustion liner 108.